Method and apparatus for maintaining uplink synchronization and reducing battery power consumption

ABSTRACT

A Node-B sends a polling message to a wireless transmit/receive unit (WTRU). The WTRU sends an uplink synchronization burst in response to the polling message without contention. The Node-B estimates an uplink timing shift based on the synchronization burst and sends an uplink timing adjustment command to the WTRU. The WTRU then adjusts uplink timing based on the uplink timing adjustment command. Alternatively, the Node-B may send a scheduling message for uplink synchronization to the WTRU. The WTRU may send a synchronization burst based on the scheduling message. Alternatively, the WTRU may perform contention-based uplink synchronization after receiving a synchronization request from the Node-B. The WTRU may enter an idle state instead of performing a handover to a new cell when the WTRU moves to the new cell. A discontinuous reception (DRX) interval for the WTRU may be set based on activity of the WTRU.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional applicationSer. No. 11/689,771, which was filed Mar. 22, 2007, which claims thebenefit of U.S. Provisional Application No. 60/785,491 filed Mar. 24,2006, which is incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to wireless communication systems. Moreparticularly, the present invention is related to a method and apparatusfor maintaining uplink synchronization and reducing battery powerconsumption of a wireless transmit/receive unit (WTRU).

BACKGROUND

In a conventional third generation partnership project (3GPP) system,there are four non-idle radio resource control (RRC) states roughlycorresponding to four levels of WTRU activity: a dedicated channel (DCH)cell level (Cell_DCH) state, a forward access channel (FACH) cell level(Cell_FACH) state, a paging channel (PCH) cell level (Cell_PCH) state,and a universal terrestrial radio access network (UTRAN) registrationarea (URA) PCH (URA_PCH) state. In a Cell_DCH state, a WTRU has adedicated physical channel for data transport. In a Cell_FACH state, nodedicated channel is allocated to the WTRU, but the WTRU may use arandom access channel (RACH) and a FACH channel for conveying andreceiving signaling as well as user plane data. It is not efficient tosend a large amount of user plane data in the Cell_FACH state. ACell_PCH state reduces battery consumption by only listening to a PCH ina discontinuous reception (DRX) mode. As with the Cell_DCH and Cell_FACHstates, the location of a WTRU in the Cell_PCH state is known at thecell level. A WTRU in the Cell_PCH state temporarily enters a Cell_FACHstate when it relocates to a new cell in order to communicate its newlocation information. A URA_PCH state is similar to the Cell_PCH state,except that in the URA_PCH state the network is only informed when theWTRU moves to a new URA. When a WTRU changes cells, the WTRU generallystays in the same state. Currently, handovers in the Cell_DCH state arenetwork-directed.

A WTRU that is in an active state has a non-access stratum (NAS)connectivity so that the WTRU may communicate to nodes in a corenetwork. A WTRU in an active state also has an access stratum (AS)connectivity such that a radio bearer configuration, (e.g., WTRUcapability exchange, ciphering, or the like), has been completed for theWTRU.

A WTRU in an idle state consumes less power and resources than a WTRU ina low-power active state. One important characteristic of a WTRU in anidle state is that the WTRU does not have to participate in an activemode handover. In other words, when a WTRU in an idle state moves fromone cell to another, the WTRU does not configure radio bearers with thenew cell if the WTRU remains in an idle state.

One of the goals in a next generation wireless communication system ismaintaining an “always on” connectivity. However, for a battery-poweredWTRU, battery power consumption is an issue. The “always on”connectivity is a desirable feature, but this tends to shorten thebattery life.

Currently in 3GPP, a WTRU maintains uplink synchronization whenever ithas a dedicated channel to a base station. The WTRU always maintainsuplink synchronization in a Cell_DCH state. The WTRU also resynchronizesits uplink any time it has a new set of dedicated channels disjoint fromits prior set. Maintaining uplink synchronization, (conventionally viaRACH transmissions), is one of the sources for consuming the batterypower of the WTRU.

Therefore, it would be desirable to provide a scheme for maintaininguplink synchronization efficiently and reducing battery powerconsumption while the WTRU is in an active state.

SUMMARY

The present invention is related to a method and apparatus formaintaining uplink synchronization and reducing battery powerconsumption of a WTRU. A Node-B sends a polling message to a WTRU. TheWTRU sends an uplink synchronization burst in response to the pollingmessage without contention. The Node-B estimates an uplink timing shiftbased on the uplink synchronization burst and sends an uplink timingadjustment command to the WTRU without contention. The WTRU then adjustsuplink timing based on the uplink timing adjustment command.Alternatively, the Node-B may send a scheduling message for uplinksynchronization to the WTRU. The WTRU may send the uplinksynchronization burst based on the scheduling message. Alternatively,the WTRU may perform contention-based uplink synchronization afterreceiving a synchronization request from the Node-B. The WTRU may enteran idle state instead of performing a handover to a new cell when theWTRU moves to the new cell. A DRX interval for the WTRU may be set basedon activity of the WTRU.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way of exampleand to be understood in conjunction with the accompanying drawingswherein:

FIG. 1 is a signaling diagram of a process for maintaining uplinksynchronization using a contention free procedure in accordance with oneembodiment of the present invention;

FIG. 2 is a signaling diagram of a process for maintaining uplinksynchronization using a contention free procedure in accordance withanother embodiment of the present invention;

FIG. 3 is a signaling diagram of a process for uplink synchronizationusing a contention-based procedure in accordance with the presentinvention; and

FIG. 4 is a block diagram of a Node-B and a WTRU configured inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

When referred to hereafter, the terminology “WTRU” includes but is notlimited to a user equipment (UE), a mobile station (STA), a fixed ormobile subscriber unit, a pager, a cellular telephone, a personaldigital assistant (PDA), a computer, or any other type of user devicecapable of operating in a wireless environment. When referred tohereafter, the terminology “Node-B” includes but is not limited to abase station, a site controller, an access point (AP), or any other typeof interfacing device capable of operating in a wireless environment.

The present invention is applicable to any wireless communicationsystems including, but not limited to, wideband code division multipleaccess (WCDMA) and long term evolution (LTE) of 3GPP cellular networksbeyond 3GPP Release 7.

FIG. 1 is a signaling diagram of a process 100 for maintaining uplinksynchronization using a contention-free procedure in accordance with oneembodiment of the present invention. For uplink synchronization, aNode-B 152 sends a polling message to a WTRU 154 to request transmissionof an uplink synchronization burst (step 102). The WTRU 154 may receivethe polling message either during registration or via broadcasting afterregistration. The polling message indicates a specific time, (e.g., asystem frame number or transmission time interval (TTI)), and/orresource for sending the uplink synchronization burst so that thespecific WTRU may send the uplink synchronization burst withoutcontending against other WTRUs. In response to the polling message, theWTRU 154 sends an uplink synchronization burst based on the parameters,(e.g., a specific time, a resource, or the like), included in thepolling message (step 104). The Node-B 152 receives the uplinksynchronization burst and estimates an uplink timing shift based on theuplink synchronization burst (step 106). The Node-B 152 sends an uplinktiming adjustment command to the WTRU 154 (step 108). The WTRU 154 thenadjusts uplink timing based on the uplink timing adjustment command(step 110).

The polling message may include uplink interference information so thatthe WTRU 154 may use the information in determining uplink transmitpower for the uplink synchronization burst. Alternatively, the Node-B152 may explicitly indicate an uplink transmit power for the uplinksynchronization burst. The Node-B 152 may send the polling message via adownlink common control channel granting an access to an uplink sharedchannel for the uplink synchronization burst.

Alternatively, to save an additional power, the WTRU 154 may enter a DRXmode and wake at predetermined intervals for either paging or uplinkshared channel allocation. If the WTRU 154 enters a DRX mode, the Node-B152 does not need to send the polling messages to the WTRU 154 veryoften. The network configures a periodicity on how often the Node-B 152should send the polling message to the WTRU 154. This periodicityinformation can be sent to the WTRU 154 through a broadcast message. Inthis way, the WTRU 154 may only wake up at the moment when the pollingmessage is expected. After listening to the polling message and performthe necessary uplink transmissions, the WTRU 154 reenters the DRX modein order to save the battery power.

The polling message may address several WTRUs containing parameters forseveral polled WTRUs to send their uplink synchronization bursts. Apolling rate may be different for each WTRU. The polling rate may bedetermined based on the estimated clock drift and/or mobility of theWTRUs. The polling rate may be adaptively changed by either the WTRU154, (via a request to the Node-B 152), or the Node-B 152. The pollingrate may be different for each RRC (or medium access control (MAC))state of the WTRU 154. The polling rate may increase over time, (e.g.,exponentially), as the period of inactivity of the WTRU 154 increases.The Node-B 152 may use the results of the uplink synchronization as onefactor in adaptively changing the polling rate for the WTRU 154. Anuplink channel allocation for the uplink synchronization burst providedby the polling message may be periodic or may optionally indicateduration of the uplink channel.

Since the WTRU 154 in the active state is already known to the Node-B152 and the Node-B 152 can uniquely identify the WTRU 154 via thescheduled times for the WTRU 154, the WTRU 154 may omit a cell ID or aWTRU ID, (e.g., a control radio network temporary identity (C-RNTI)), inthe uplink synchronization burst. This will reduce an overhead.

Alternatively, the Node-B 152 may include a short, (preferably random),identifier, tag or a sequence number in the polling message, and theWTRU 154 may use the same short identifier, tag or sequence number inthe uplink synchronization burst. Since this identifier, tag, orsequence number is smaller than other forms of identification, (e.g., acell ID or a C-RNTI), the overhead is reduced.

FIG. 2 is a signaling diagram of a process 200 for maintaining uplinksynchronization using a contention-free procedure in accordance withanother embodiment of the present invention. A Node-B 252 generates aschedule for uplink synchronization for a WTRU 254 and sends ascheduling message for uplink synchronization to the WTRU 254 (step202). The scheduling message may include a schedule for several WTRUs.Uplink synchronization is performed at predetermined times using apredetermined resource specified in the scheduling message. The Node-B252 may signal the resource for uplink synchronization to the WTRU 254prior to the scheduled synchronization time. The scheduling message mayinclude uplink interference information or uplink transmit powerinformation. The uplink transmit power information may be for a group ofWTRUs if they are in a similar situation. Alternatively, the uplinktransmit power information may be for each WTRU or may just be used as areference. The scheduling message may be transmitted via a downlinkcommon control channel granting an access to an uplink shared channelfor the synchronization burst.

The WTRU 254 sends an uplink synchronization burst based on thescheduling message (step 204). The WTRU 254 may optionally indicate thenext synchronization time in the uplink synchronization burst, (i.e.,the synchronization burst payload may include a field indicating thenext synchronization time). This synchronization time may be viewed as arecommendation by the Node-B 252, and the Node-B 252 may modify theschedule or the recommendation by sending a signal via a downlinksignaling channel, (e.g., a shared control channel). The WTRU 254 mayalso send a scheduling request informing the amount of data waiting fortransmission in the WTRU 254. The WTRU 254 may also send measurementresults such as a channel quality indicator (CQI).

The Node-B 252 estimates an uplink timing shift based on the uplinksynchronization burst (step 206). The Node-B 252 sends an uplink timingadjustment command to the WTRU 254 (step 208). The WTRU 254 then adjustsuplink timing based on the uplink timing adjustment command (step 210).

Since the WTRU 254 in an active state is already known to the Node-B 252and the Node-B 252 can uniquely identify the WTRU 254 via the scheduledtimes for the WTRU 254, the WTRU 254 may omit a cell ID or a WTRU ID,(e.g., a C-RNTI), in the uplink synchronization burst. This will reducean overhead.

Alternatively, the Node-B 252 may include a short, (preferably random),identifier, tag or a sequence number in the scheduling message, and theWTRU 254 may use the same short identifier, tag or sequence number inthe uplink synchronization burst. Since this identifier, tag, orsequence number is smaller than other forms of identification, (e.g., acell ID or a C-RNTI), the overhead is reduced.

FIG. 3 is a signaling diagram of a process 300 for uplinksynchronization using a contention-based procedure in accordance withthe present invention. A Node-B 352 sends a synchronization requestmessage to a WTRU 354 instructing or recommending the WTRU 354 toperform an uplink synchronization procedure during the WTRU 354 is in anactive state (step 302). The synchronization request message may addressmultiple WTRUs. The synchronization request message may include aspecific time and/or resource for the WTRU to send the synchronizationburst. The synchronization request message may include uplinkinterference information or uplink transmit power information. Thesynchronization request message may be transmitted via a downlink commoncontrol channel granting an access to an uplink shared channel for thesynchronization burst.

In response, the WTRU 354 performs the conventional contention-basedprocedure for uplink synchronization. The WTRU 354 sends an uplinktransmission, (e.g., an RACH preamble), to the Node-B 352, (e.g., via anRACH), using a contention-based mechanism, (e.g., a slotted Alohamechanism) (step 304). Either non-synchronized or synchronized RACH canbe used for this uplink transmission, which is indicated either throughan RRC signaling or by the synchronization request message from theNode-B 352. The Node-B 352 receives the uplink transmission andestimates an uplink timing shift based on the uplink transmission (step306). The Node-B 352 sends an uplink timing adjustment command to theWTRU 354 (step 308). The WTRU 354 then adjusts uplink timing based onthe uplink timing adjustment command (step 310).

The Node-B 352 may include a short, (preferably random), identifier, tagor a sequence number in the uplink synchronization request message, andthe WTRU 354 may use the same short identifier, tag or sequence numberin the uplink synchronization burst.

The Node-B 352 may designate a frame, a sub-frame or a timeslot in whichthe uplink synchronization procedure (or random access procedures)should be performed while the WTRU 354 is in an active state. Thedesignated frame, sub-frame or timeslot is different than the frames,sub-frames or timeslots that are used to perform the uplinksynchronization procedure (or random access procedures) during the WTRU354 is in an idle state, (i.e. different than the RACH timeslots). Thedesignation of the frame, sub-frame or timeslot may be performed viaprior signaling, (e.g., broadcast messages), or via pre-configuration.The Node-B 352 may provide different service levels or meet thedifferent performance requirements or targets for WTRUs in an activestate as opposed to WTRUs in an idle state. When a WTRU 354 is in anactive state, in order to support the active traffic, more tightlymaintained uplink synchronization is required. Therefore, the WTRU 354may need to send uplink synchronization transmission more frequentlycompared to an idle state which requires less tight uplinksynchronization since there is no active traffic going on.

In all the above embodiments, the Node-B may include a flag in thepolling message, the scheduling message or the synchronization requestmessage to indicate whether it is mandatory or optional that the WTRUperforms the procedure for uplink synchronization. Commanding the WTRUto perform uplink synchronization, (i.e., setting the flag to“mandatory”), is useful when the Node-B needs to send packets to theWTRU, (e.g., high speed downlink packet access (HSDPA)), since the WTRUneeds to be uplink synchronized in order to send a hybrid automaticrepeat request (H-ARQ) positive feedback. Preferably, the flag isincluded within the polling message, the scheduling message or thesynchronization request message. If the flag indicates the uplinksynchronization is optional, the WTRU may or may not perform the uplinksynchronization procedure.

FIG. 4 is a block diagram of a Node-B 400 and a WTRU 450 configured inaccordance with the present invention. The Node-B 400 includes an uplinksynchronization controller 402 and a transceiver 404. The WTRU 450includes a transceiver 452 and an uplink synchronization controller 454.The uplink synchronization controller 402 generates a polling message, ascheduling message or a synchronization request message for the WTRU450. The transceiver 404 transmits the polling message, the schedulingmessage or the synchronization request message to the WTRU 450. Thetransceiver 452 of the WTRU 450 receives the polling message, thescheduling message or the synchronization request message, and sends anuplink synchronization burst based on the polling message, thescheduling message or the synchronization request message to the Node-B400.

The uplink synchronization controller 402 estimates an uplink timingshift based on an uplink synchronization burst transmitted by the WTRU450, and generates an uplink timing adjustment command. The transceiver404 then sends the uplink timing adjustment command to the WTRU 450. Theuplink synchronization controller 454 of the WTRU 450 then adjustsuplink timing based on the uplink timing adjustment command.

In accordance with another embodiment of the present invention, a WTRUmay use cell reselection as a trigger to go from a low-power activestate to an idle state. When a WTRU, through its cell search and cellreselection procedures, determines that the WTRU should move to a newcell, the WTRU may enter an idle state, instead of performing a handoverand radio bearer reconfiguration. In this manner, the WTRU may conservepower by avoiding the control signaling associated with the handover andradio bearer reconfiguration.

In accordance with yet another embodiment of the present invention, aDRX interval, (i.e., the WTRU's wake-up time intervals for reception),may be configured adaptively according to a service level, (i.e.,activity of the WTRU). The DRX interval is increased as the period ofinactivity of the WTRU increases subject to a predetermined maximumvalue. The DRX interval may be increased exponentially. Preferably, thenetwork determines the DRX interval and signals it to the WTRU.

Alternatively, the WTRU may inform the Node-B whether the WTRU iscurrently powered by a battery or a constant power supply, so that theDRX interval is set accordingly. The WTRU may inform the Node-B of itscurrently remaining battery capacity and other characteristics, (such asconsumed power in transmitting data), that may assist the Node-B incomputing the estimated battery life. The Node-B then sets up powersaving policies, (e.g., DRX interval), for the WTRU based on theinformation.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention. Themethods or flow charts provided in the present invention may beimplemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) module.

1-6. (canceled)
 7. A method performed by a wireless transmit/receiveunit (WTRU), the method comprising: receiving discontinuous reception(DRX) control information from a wireless network, the DRX controlinformation indicating a time interval that the WTRU should monitor adownlink control channel; receiving a control message on the downlinkcontrol channel while monitoring the downlink control channel accordingto the DRX control information, wherein the control message isassociated with an identifier of the WTRU, the control messageindicating that the WTRU should transmit a random access preamble to thewireless network; transmitting the random access preamble to thewireless network in response to receiving the control message; andreceiving a timing adjustment command from the wireless network.
 8. Themethod of claim 7, further comprising adjusting uplink timing accordingto the timing adjustment command.
 9. The method of claim 8, furthercomprising sending a hybrid automatic repeat request (H-ARQ) feedback tothe wireless network after adjusting uplink timing according to thetiming adjustment command.
 10. The method of claim 7, wherein theidentifier includes a sequence number that uniquely identifies the WTRU.11. The method of claim 7, wherein the control message indicates aresource to be used by the WTRU for transmitting the random accesspreamble.
 12. The method of claim 11, wherein the resource includes asubframe to be used by the WTRU to transmit the random access preamble.13. The method of claim 7, further comprising entering a DRX mode whilethe WTRU is in an active state.
 14. The method of claim 7, wherein therandom access preamble is sent using a contention-based mechanism.
 15. Awireless transmit/receive unit (WTRU) comprising: a transceiver, and aprocessor coupled to the transceiver, the processor configured to:receive discontinuous reception (DRX) control information from awireless network, the DRX control information indicating a time intervalthat the WTRU should monitor a downlink control channel; receive acontrol message on the downlink control channel while monitoring thedownlink control channel according to the DRX control information,wherein the control message is associated with an identifier of theWTRU, the control message indicating that the WTRU should transmit arandom access preamble to the wireless network; transmit the randomaccess preamble to the wireless network in response to receiving thecontrol message; and receive a timing adjustment command from thewireless network.
 16. The WTRU of claim 15, wherein the processor isfurther configured to adjust uplink timing according to the timingadjustment command.
 17. The WTRU of claim 16, wherein the processor isfurther configured to send a hybrid automatic repeat request (H-ARQ)feedback to the wireless network after adjusting uplink timing accordingto the timing adjustment command.
 18. The WTRU of claim 15, wherein theidentifier includes a sequence number that uniquely identifies the WTRU.19. The WTRU of claim 15, wherein the control message indicates aresource to be used by the WTRU for transmitting the random accesspreamble.
 20. The WTRU of claim 19, wherein the resource includes asubframe to be used by the WTRU to transmit the random access preamble.21. The WTRU of claim 15, wherein the processor is further configured toenter a DRX mode while the WTRU is in an active state.
 22. The WTRU ofclaim 15, wherein the random access preamble is sent using acontention-based mechanism.
 23. A wireless transmit/receive unit (WTRU)comprising: a transceiver, and a processor coupled to the transceiver,the processor configured to: receive discontinuous reception (DRX)control information from a wireless network, the DRX control informationindicating a time interval that the WTRU should monitor a downlinkcontrol channel; receive a control message on the downlink controlchannel while monitoring the downlink control channel according to theDRX control information, wherein the control message is associated withan identifier of the WTRU, the control message indicates that the WTRUshould transmit a random access preamble to the wireless network, andthe control message is indicative of a time and resource for the WTRU totransmit the random access preamble; transmit the random access preambleto the wireless network in response to receiving the control message;and receive a timing adjustment command from the wireless network. 24.The WTRU of claim 23, wherein the processor is further configured toadjust uplink timing according to the timing adjustment command.
 25. TheWTRU of claim 23, wherein the processor is further configured to send ahybrid automatic repeat request (H-ARQ) feedback to the wireless networkafter adjusting uplink timing according to the timing adjustmentcommand.
 26. The WTRU of claim 23, wherein the time for the WTRU totransmit the random access preamble indicated by the control messagecomprises one or more subframes.